Embodiments of the present application generally relate to resettable fuses. More particularly, but not exclusively, embodiments of the present application relate to solid state resettable fuse having both an elevated voltage and elevated electrical current rating.
Overcurrent protection devices traditionally have been utilized in the protection of cables, contactors, switches, equipment and individuals from hazards associated with excessive electrical current, including, for example, short circuits, overloading, mismatched loads, or device failure. Protection from the potentially dangerous and/or damaging effects of such overcurrent events can be implemented in a number of different manners, including, for example, by traditional fuses or mechanical circuit breakers. For example, traditional fuses may have a sacrificial element, such as a filament, that melts and/or breaks when the electrical current flowing therethrough exceeds a threshold limit, thereby facilitating a break or interruption in the associated circuit. Similarly, certain breakers may utilize a bimetallic strip that, when current flowing therethrough exceeds a threshold value, bends or otherwise deforms to a position that can contact another component of the breaker that triggers the tripping of the breaker. However, after such overcurrent protection devices trip or interrupt the circuit, the overcurrent protection devices typically need to be serviced before the operation of the circuit can be restored. Yet, such servicing often involves the manual replacement of the broken fuse and/or resetting of the breaker. Such manual resetting and/or replacement of traditional overcurrent protection devices can be particularly challenging and costly when the overcurrent protection device is remote, hard to reach, and labor intensive.
Positive temperature coefficient (PTC) resettable fuses can also be used to protect against overcurrent faults in electronic circuits, including, for example, polymer positive temperature coefficient (PPTC) resettable fuses. PPTC resettable fuses can be constructed from a blend of polymer and conductive particles that can create networks of conductive paths through which electrical current may flow through the PPTC resettable fuse during normal operating conditions. However, when the electrical current flowing through the PPTC resettable fuse exceeds a threshold current limit, the temperature of the PPTC resettable fuse may be elevated beyond a threshold temperature. Such elevations in temperature beyond the threshold temperature can trip the PPTC resettable fuse, wherein the electrical resistance of the PPTC resettable fuse relatively rapidly increases by several orders of magnitude. For example, in certain situations, when the temperature of the PPTC resettable fuse is elevated above the threshold temperature, the electrical resistance of the PPTC resettable fuse can be hundreds or thousands of ohms. Further, as power sources can have a finite voltage, such an elevation in the electrical resistance of the PPTC resettable fuse can subsequently reduce the electrical current flowing through the PPTC resettable fuse.
As traditional PTC resettable fuses have relatively limited voltage or current ratings, PTC resettable fuses typically have difficulty in accommodating both a relatively high current and a relatively high voltage. For example, when the voltage rating of a PTC resettable fuse is relatively low, such as, for example, around 15 volts (V), the maximum fault current at which the PTC resettable fuse will withstand at rated voltage without damaging the fuse, also referred to as maximum current, can be as high as 50 A. However, as the voltage rating of resettable fuses increase, the maximum current of those fuses typically decreases. For example, certain PTC resettable fuses having a voltage rating of around 72 volts to around 120 volts can have a maximum current of only 6 amps (A) to 7.5 amps. Conversely, while certain PTC resettable fuses having a voltage rating of 240 V, the associated maximum current may only be around 4 amps. Further, when the voltage rating of such resettable fuses further increases to hundreds of volts, the maximum current of PTC resettable fuses often are reduced to tens to hundreds of milliamps (mA). For example, certain PTC resettable fuses having a current rating of 1000 volts can have a maximum current of only 17 mA. Accordingly, the inability to attain both high current and high voltage can limit the application of PTC resettable fuses to certain technologies and devices.